By LARRY LANGE, P-I REPORTER

Updated 10:00 pm, Wednesday, March 4, 2009

The state Senate overwhelmingly approved replacing the Alaskan Way Viaduct with a $4.2 billion tunnel after a short debate Wednesday that one tunnel backer said resulted from a previous agreement among three major government entities.

"I'll bet the whole debate didn't last 10 minutes," said Sen. Ed Murray, D-Seattle, one of the sponsors of Senate Bill 5768 designating the tunnel as the replacement.

Senators approved the measure 43-6. It now goes to the House, where its future is less certain.

The tunnel was agreed to as the replacement by Gov. Chris Gregoire, Seattle Mayor Greg Nickels and King County Executive Ron Sims, after downtown, business and labor interests formed a coalition to push for it.

The bill calls replacement of the 1953-vintage viaduct "a matter of urgency for the safety of Washington's traveling public" and directs the state to expedite design work and environmental-impact analyses to replace the six-lane, double-deck highway with a 54-foot-diameter tunnel.

The new four-lane highway also would be double-decked inside the tunnel, which would be bored under First Avenue and extend from the sports stadiums to Harrison Street, north of the Battery Street Tunnel.

The tunnel was the costliest of any options discussed during the past year. State, city and county transportation departments said in December that they wanted to complete further studies on a less expensive elevated highway design and a "surface-transit" design that would disperse vehicles onto surface streets and more people onto buses.

But tunnel advocates persuaded Gregoire, Nickels and Sims to choose that option.

Murray said the overwhelming Senate vote came after he argued that the state had appropriated money for the replacement four years ago and had "struggled with decisions about what we would build there."

With the January agreement, "it's time to move forward," he said, and in the Senate the agreement "drove the positive votes, rather than preference for any particular option."

Advocates say that most of a tunnel could be dug underground without disrupting traffic on the old structure until final connections were made. They also say removing the viaduct would open new waterfront vistas, create new public spaces and increase land values.

Cost overruns remain a big issue with some skeptics who worry about another high-priced "Big Dig" like the one on Boston. One critic is House Speaker Frank Chopp, D-Seattle, who strongly advocates building a new elevated highway in a structure that would also include a park, offices and retail spaces.

The cost of that option was estimated at $2.4 billion; Chopp said it would create new development and public space along with the highway. Some have argued that his design raises safety issues and wouldn't attract development.

Chopp, who is powerful enough to stop the tunnel proposal, has not said whether he will. But he has expressed concerns about cost overruns and the fact that there would be fewer traffic lanes than on the present structure. He could not be reached Wednesday.

The bill passed Wednesday endorses the tunnel concept and calls for a study of tolls on it, to be completed next year.

Lawmakers also approved a measure Wednesday designating what state highways will get about $340 million in federal economic-stimulus money, but they did not provide any funding for improvements to the Mercer Street corridor and no more money for Spokane Street, parts of Seattle's contribution to the viaduct replacement.

The city said it will now look to other parts of the federal stimulus package, and possibly to other sources, to fund the controversial Mercer project.

"There seems to be support for the tunnel in the House," she said, but it is "anecdotal." She said cost overruns are an issue, but "we are not making other cities responsible for cost overruns on their state projects." She said the tunnel should be done on a design-build contract to save time and cost.

Another member of the House committee, Rep. Mary Lou Dickerson, D-Seattle, said she will listen to people with an interest in the viaduct and to committee testimony before deciding how to vote.

"My biggest concern is ... about access to (state Route 99) for residents and businesses in the northwest part of Seattle, because the current plan calls for closure of the exits and entrances" to the highway and new tunnel from Western and Elliott avenues.

Several tunnel opponents are circulating a city initiative to put the project to a vote; others have reminded officials that a tunnel proposal was rejected by city voters in a 2007 advisory election.

Maritime interests have objected that a tunnel couldn't be used for fuel shipments, and others say a tunnel would be built near an earthquake fault, where there's some risk a tremor could create a tidal wave that could flood the tunnel.